Holders for stacks and sheets are well known and used in many different environments. One particular use is in electrophotographic devices to store the paper onto which the copied image is formed. For example, European Application No. 0 102 202 A3 published on Mar. 7, 1984 describes a holder for a stack of sheets with a separating means for separating the sheets that are returned to the holder from those which have yet to leave the holder to be copied. That application describes numerous document feeding devices and paper aligners which utilize stack holders.
Holders of the type which include a separator are described in United Kingdom Pat. No. 1,599,774 which shows a holder in which sheets fed from the holder are returned to it after being processed. The separating means separates the returned sheets from those sheets which are still to be fed from the holder, and being placed back on the stack of sheets for this purpose whenever a detector reacts. In that holder, however, the presence or absence of sheets therein cannot be detected.
Such detecting means are very desirable so that it can be determined when sheet processing can start and, if the sheets are not to be returned to the holder after processing when all of the sheets have been processed. It is, therefore, an object of this invention to provide simple means with which the presence or absence of sheets in the holder can be detected.